Structure and union declarations types are same as that found in C language. One can use the structure data types to declare complex data type, which is nothing but a collection of other data types. Example would be a ethernet packet can declared as a struct with variables for each of the fields of the packet. A struct can be assigned as a whole, and passed to or from a function or task as a whole. typedef can used be used with struct as in C language. structs and unions can be

• packed : A packed structure consists of bit fields, which are packed together in memory without gaps.
• unpacked : An unpacked structure has an implementation-dependent packing, normally matching the C compiler.
• tagged : An Tagged union is a type-checked union.

  1 `timescale 1ns/10ps
  2 
  3 // Type define a struct, and put it outside module
  4 // So that other modules can also use it
  5 typedef struct {
  6   byte a;
  7   reg  b;
  8   shortint unsigned c;
  9 } myStruct;
 10 
 11 module struct_data ();
 12 
 13 // Define a local struct.
 14 struct {
 15   byte a;
 16   reg b;
 17   shortint unsigned c;
 18 } myLocalStruct = '{11,1,101};
 19 
 20 // When defined typedef, we can use as new data type
 21 myStruct object = '{10,0,100};
 22 
 23 initial begin
 24   $display ("a = %b b = %b c = %h", object.a, object.b, object.c);
 25   $display ("a = %b b = %b c = %h", myLocalStruct.a, 
 26        myLocalStruct.b, myLocalStruct.c);
 27    #1  $finish;
 28 end
 29 
 30 endmodule

 a = 00001010 b = 0 c = 0064
 a = 00001011 b = 1 c = 0065

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Deepak Kumar Tala - All rights reserved

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